Field of the Invention
The invention relates to a device for correcting a skew of skewed printing plates on a plate cylinder of a rotary printing machine, having a front clamping bar for holding a leading edge of a printing plate and a rear clamping bar for holding a trailing edge of a printing plate. In order to be able to correct a skewed position of the printing image, the printing plate, together with the printing-plate holding device, must be capable of skew adjustment.
The published German Patent Document DE 41 34 365 A1 has already disclosed a device for correcting the skew of a printing plate, wherein the front clamping bar can be pivoted about a centrally disposed pivot point, and wherein the rear clamping bar is mounted on a freely pivotable lower bar. The corresponding entrainment of the rear clamping bar during a pivoting movement of the front clamping bar is effected by an angle lever and a coupler or connecting rod, the angle lever having a linear guide.
The clamping force for holding the printing plate on the rear clamping bar is applied by tensioning screws, which are supported on an axially adjustable tensioning wedge.
The published German Patent Document DE 39 36 446 A1 has also already disclosed the practice of providing known tensioning springs, which are supported by one end on a clamping bar and by the other end on the side wall, of the plate cylinder channel, which is fixed to the cylinder.
In this case, it is disadvantageous that, in the event of a skewed position of the rear clamping bar, the tensioning springs have different tensioning travel distances distributed over the axial length, and therefore different tensioning forces occur.
It is accordingly an object of the invention to provide a device for correcting the skew of a printing plate, the correction device being of compact construction.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a device for correcting a skew of a skewed printing plate on a plate cylinder of a rotary printing machine, comprising a front clamping bar for holding a leading edge of the printing plate; and a rear clamping device including at least one rear clamping bar for holding a trailing edge of the printing plate, an axially guided lower bar and a pivoting strip mounted so as to be pivotable about a first pivot point on the lower bar; the front clamping bar being pivotable about a second pivot point disposed approximately centrally in an axial extent of a cylinder channel formed in the plate cylinder, and the at least one rear clamping bar being mounted on the pivoting strip so that the at least one rear clamping bar is pivotable in circumferential direction about a third pivot point.
In accordance with another feature of the invention, at least one compression spring for simultaneously clamping and tensioning an end of the printing plate is braced against the pivoting strip and against the at least one rear clamping bar.
In accordance with a further feature of the invention, the second pivot point about which the front clamping bar is pivotable has an axis extending through a region of the leading edge of the printing plate.
In accordance with an added feature of the invention, the first pivot point is disposed on an axis extending from the pivoting strip to the rear clamping bar at a region of the trailing edge of the printing plate.
In accordance with a concomitant feature of the invention, the first pivot point is disposed at least approximately centrally to the cylinder channel in the axial direction thereof.
An advantage of the invention resides, particularly, in that the device for correcting skew is of compact construction. In this regard, the tensioning springs for the rear clamping rail are braced against the pivoting strip which moves in synchronism with the conjointly moving rear clamping bar, so that no transverse forces act upon the spring elements.
In an advantageous construction, only a single lever is provided for entraining the rear clamping bar.
In order to leave the circumferential register unchanged during the correction to the skew of the printing plate, the second or front pivot point is located centrally on an axis extending to a region of the leading edge of the printing plate, because a previously set circumferential register thereby remains virtually unchanged. Advantageous to the same extent is the disposition of the axis through the first pivot point for the rear pivoting strip, which extends to the region of the trailing edge of the printing plate.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a device for correcting skew of printing plates on a plate cylinder of a rotary printing machine, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, wherein: